1. Field of the Invention
The present invention relates to coil devices having wires wound around cores and to a method for manufacturing the same. More particularly, the present invention relates to a wire-wound coil device provided with terminal electrodes on flanges provided at the ends of the reel of a core.
2. Description of the Related Art
As shown in FIG. 8, a typical wire-wound coil device has a core 53 including a reel 51, a pair of flanges 52 disposed at the ends of the reel 51, a wire 54 wound around the reel 51, and terminal electrodes 55 provided at the lower portions of the flanges 52 and connected to the ends of the wire 54.
A problem has been found in the above-described wirewound coil device in that as the size of the coil device is reduced, the area of the terminal electrodes 55 (i.e., the size of electrodes) is reduced, and therefore, adhesion of the coil device, when mounted on a printed circuit board or other device by soldering, is reduced, thereby lowering reliability when the coil device is mounted.
Other typical wire-wound coil devices have configurations, for example, as described below.
A coil device shown in FIG. 9 is configured such that each terminal electrode 55 provided on a leg 56 of a core 53 is provided such that the terminal electrode 55 is disposed to cover the leg 56 to a level of an end surface 56a (the outer surface) which is higher than that of a surface 56b (the inner surface) opposite to the end surface 56a of the leg 56, and the upper edges of the terminal electrode 55 are inclined at side surfaces 56c (the remaining side surfaces) of the leg 56.
Another coil device shown in FIG. 10 is configured such that the terminal electrodes 55 are disposed on a pair of flanges 52 provided at the ends of the core 53 so that each terminal electrode 55 extends over an entire bottom surface 52a to an end surface 52c of the flange 52.
The components referred to in FIGS. 9 and 10 are the same as or have the same functions as the component shown in FIG. 8.
In the coil device shown in FIG. 9, the terminal electrodes 55 are located at a high level of each outer end 56a of the legs 56 so as to increase the size of the electrodes, thereby improving an adhesive effect in the mounted state by soldering.
In the coil device shown in FIG. 10, the terminal electrodes 55 are arranged to extend over the entire bottom surface 52a to the end surface 52c of the pair of flanges 52 provided at the ends of the core 53 so as to increase the size of the electrodes, thereby improving an adhesive effect in the mounted state by soldering.
In the coil devices of FIGS. 9 and 10, the terminal electrodes 55 are arranged to extend to a high level of the outer end surfaces 56a of the legs 56 (see FIG. 9) or to a high level of the outer end surfaces 52c of the flanges 52 (see FIG. 10), respectively. In this case, the terminal electrodes 55 provided on the outer end surfaces 56a of the legs 56 in FIG. 9 or on the outer end surfaces 52c of the flanges 52 in FIG. 10 vertically interrupt magnetic fluxes, thereby adversely affecting the Q factor.
When an electrode is provided, as in the coil devices shown in FIGS. 9 and 10, having the upper edges thereof being disposed at different levels, the manufacturing cost is increased because the device to be manufactured must be maintained inclined during the manufacturing process, or a particular paste-applying device for pasting the electrode must be used.
In addition to the increased cost, the manufacturing process is complex. As the size of the device is further reduced, the manufacturing process of the coil device having the configuration shown in FIGS. 9 and 10 in which the upper edges of the electrode are disposed at different levels becomes increasingly difficult.
To overcome the above-described problems, preferred embodiments of the present invention provide a wire-wound coil device and a method for manufacturing the same, in which reliable mounting is achieved by providing large electrode areas even when the size of the coil device is reduced, and a high Q factor in the coil device is maintained.
According to an aspect of preferred embodiments of the present invention, a coil device includes a core including a reel and a pair of flanges provided at the ends of the reel, a terminal electrode disposed on each of the flanges of the core, and a wire wound around the reel of the core, thereby defining a coil, each end of the wire being connected to the terminal electrode. The terminal electrode includes a bottom-surface electrode provided on a bottom surface of the flange, side-surface electrodes provided on side surfaces of the flange, and an end-surface electrode provided at the lower part of an end surface of the flange. The end-surface electrode is provided on the end surface of the flange so that the upper edge of the end-surface electrode is disposed at a first level which is substantially the same as that of the upper edges of the side-surface electrodes in the vicinity of the boundaries between the end surface and each side surface of the flange and is disposed at a second level lower than the first level at an approximate center of the end surface of the flange, whereby the end-surface electrode avoids the majority of magnetic fluxes passing in an axial direction of the coil.
Each terminal electrode includes the bottom-surface electrode provided on the bottom surface of the flange, the side-surface electrodes provided on the side surfaces of the flange, and the end-surface electrode provided at the lower part of the end surface of the flange. The end-surface electrode is arranged at substantially the same height as the side-surface electrodes in the vicinity of the boundaries between the end surface and each side surface of the flange, and the end-surface electrode is arranged lower in height than the side-surface electrodes in the vicinity of the boundaries therebetween at a center of the end surface of the flange. With this configuration, an area of each terminal electrode for achieving sufficient adhesion for mounting is provided. Further, because the end-surface electrode is located spaced from the major portion of magnetic fluxes passing in an axial direction of the coil, the magnetic fluxes are not adversely affected by the end-surface electrode. With this arrangement, a high Q factor is achieved.
According to preferred embodiments of the present invention, the Q-value and the area of the terminal electrodes are balanced, and the adhesion for mounting is improved without adversely affecting the Q factor.
According to preferred embodiments of the present invention, each flange of the pair of flanges is provided with two legs at the lower portion thereof, the two legs being provided by dividing the lower portion of the flange into two parts by a groove, and being provided with the above-described terminal electrodes.
The present invention may be applied to a four-terminal-type coil device having a configuration in which each of a pair of flanges includes two legs at the lower portion thereof. This four-terminal-type coil device has terminal electrodes that operate in the same manner as the terminal electrodes of the above-described coil device according to preferred embodiments of the present invention.
According to another preferred embodiment of the present invention, a method for manufacturing a coil device is provided, the coil device including a core having a reel and a pair of flanges provided at the ends of the reel, a terminal electrode disposed on each of the flanges of the core, and a wire wound around the reel of the core, thereby forming a coil, each end of the wire being connected to the terminal electrode. The method includes the steps of providing a conductive paste for forming the terminal electrodes at a desired thickness on a substantially planar surface of a conductive-paste supporting member, dipping the core in a conductive paste layer provided on the conductive-paste supporting member, and moving back and forth at least one of the conductive-paste supporting member and the core in a direction substantially parallel to an end surface of the flange and the substantially planar surface of the conductive-paste supporting member provided with the conductive paste, thereby coating a bottom surface, side surfaces, and the end surface of the flange with the conductive paste so that the upper edge of an area on which conductive paste has been applied on the end surface of the flange is disposed at a first level which is substantially the same as that of the upper edges of areas on which conductive paste has been applied on the side surfaces in the vicinity of the boundaries between the end surface and each side surface of the flange and is disposed at a second level lower than the first level at an approximate center of the end surface of the flange. The method also includes the step of forming terminal electrodes by baking the conductive paste provided on the core.
A coil device is effectively manufactured by the method according to preferred embodiments of the present invention in which the conductive paste for forming the terminal electrodes is formed to have a desired thickness on the substantially planar surface of the conductive-paste supporting member, the core is dipped in the conductive paste layer provided on the conductive-paste supporting member, and at least one of the conductive-paste supporting member and the core is moved back and forth in a direction substantially parallel to the end surface of the flange and the substantially planar surface of the conductive-paste supporting member provided with the conductive paste, whereby the bottom surface, the side surfaces, and the end surface of the flange are effectively coated with the conductive paste so that the upper edge of the conductive-paste-coated area on the end surface of the flange is disposed at the first level which is substantially the same as that of the upper edges of the conductive-paste-coated areas on the side surfaces in the vicinity of the boundaries between the end surface and each side surface of the flange and is disposed at the second level lower than the first level at a center of the end surface of the flange. Therefore, the coil device according to preferred embodiments of the present invention are efficiently manufactured.
In the method for manufacturing a coil device according to another preferred embodiment of the present invention, a plurality of the cores held by an adhesive and elastic sheet provided on a core-holding member are brought into contact with the surface of the conductive-paste supporting member provided with the conductive paste, and at least one of the conductive-paste supporting member and the core-holding member is moved back and forth in a direction substantially parallel to the end surface of the flange and the surface of the conductive-paste supporting member provided with the conductive paste, thereby applying the conductive paste to the flanges of each core.
When the conductive paste is applied to the flanges of each core by processes in which a plurality of the cores held by the adhesive and elastic sheet provided on the core-holding member are brought into contact with the surface of the conductive-paste supporting member provided with the conductive paste, and at least one of the conductive-paste supporting member and the core-holding member is moved back and forth in a direction substantially parallel to the end surface of the flange and the surface of the conductive-paste supporting member provided with the conductive paste, the adhesive and elastic sheet reduces the dimension variations of each core in the height direction, whereby the cores are prevented from breaking and are pressed to the conductive-paste supporting member by a uniform pressing force, thereby enabling application of the conductive paste to the cores in a desired pattern.